From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 083F3C4332F for ; Mon, 17 Oct 2022 07:12:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230092AbiJQHMW (ORCPT ); Mon, 17 Oct 2022 03:12:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229597AbiJQHMS (ORCPT ); Mon, 17 Oct 2022 03:12:18 -0400 Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 71BFFCC5; Mon, 17 Oct 2022 00:12:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1665990737; x=1697526737; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=x6PiYaEhI9CWQtceoPEo/iuzEQmzk58Ipq2FJvB4zG8=; b=jUKKVqMFOxCqhnVk5ka9sAo+6nUlN4r5vCOSWAkxMscf3d2rs0jnfjWi Rc/kQHLpRTDKANMPZR6uCavG6lFf8obLGCsn5Rsm32qdtq4F9xVYZh1Rg 21UfAxBrQE30wfoAxQRLBVX/ISTdHpuQIPZDNooZipqJ5fbluIMLZd8NV BRx5fDZGk70cmbFLLF75xqRpdWGavV9YiZrQrHMhQk8c3xrOBHPLuk1pt KJFrCS+Gbhs8NX5ChjvJpDldcVU7JnvgHIaxccZMmLq2VBl3Tz2WWzr/U T8gVwzvOWgMaQzHbI+9Eupncp5+a9lEw2Wj939BbzVqXhjDy5H+MD1smy Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10502"; a="369917627" X-IronPort-AV: E=Sophos;i="5.95,190,1661842800"; d="scan'208";a="369917627" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Oct 2022 00:12:16 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10502"; a="630581889" X-IronPort-AV: E=Sophos;i="5.95,190,1661842800"; d="scan'208";a="630581889" Received: from punajuuri.fi.intel.com (HELO paasikivi.fi.intel.com) ([10.237.72.43]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Oct 2022 00:12:13 -0700 Received: from paasikivi.fi.intel.com (localhost [127.0.0.1]) by paasikivi.fi.intel.com (Postfix) with SMTP id E8E10202D5; Mon, 17 Oct 2022 10:12:10 +0300 (EEST) Date: Mon, 17 Oct 2022 07:12:10 +0000 From: Sakari Ailus To: Laurent Pinchart Cc: Prabhakar , Krzysztof Kozlowski , Rob Herring , Mauro Carvalho Chehab , Hans Verkuil , Shawn Tu , Jacopo Mondi , linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Biju Das , Lad Prabhakar Subject: Re: [PATCH v2 4/5] media: i2c: ov5645: Return zero for s_stream(0) Message-ID: References: <20221014183459.181567-1-prabhakar.mahadev-lad.rj@bp.renesas.com> <20221014183459.181567-5-prabhakar.mahadev-lad.rj@bp.renesas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 17, 2022 at 12:03:17AM +0300, Laurent Pinchart wrote: > Hi Sakari, > > On Sun, Oct 16, 2022 at 08:19:40PM +0000, Sakari Ailus wrote: > > On Sun, Oct 16, 2022 at 02:23:13AM +0300, Laurent Pinchart wrote: > > > On Sat, Oct 15, 2022 at 09:35:12PM +0000, Sakari Ailus wrote: > > > > On Sat, Oct 15, 2022 at 09:25:37AM +0300, Laurent Pinchart wrote: > > > > > On Fri, Oct 14, 2022 at 07:34:58PM +0100, Prabhakar wrote: > > > > > > From: Lad Prabhakar > > > > > > > > > > > > Always return zero while stopping the stream as the caller will ignore the > > > > > > return value. > > > > > > > > > > > > This patch drops checking the return value of ov5645_write_reg() and > > > > > > continues further in the code path while stopping stream. The user anyway > > > > > > gets an error message in case ov5645_write_reg() fails. > > > > > > > > > > Continuing all the way to pm_runtime_put() is fine, but I don't think > > > > > the function should return 0. It's not up to the driver to decide if a > > > > > failure would be useful to signal to the caller or not. > > > > > > > > If the function returns an error when disabling streaming, what is the > > > > expected power state of the device after this? > > > > > > That's up to us to decide :-) > > > > > > > The contract between the caller and the callee is that the state is not > > > > changed if there is an error. > > > > > > For most APIs, but that's not universal. > > > > > > > This is a special case as very few callers > > > > check the return value for streamoff operation and those that do generally > > > > just print something. I've never seen a caller trying to prevent streaming > > > > off in this case, for instance. > > > > > > I think the stream off call should proceed and try to power off the > > > device even if an error occurs along the way, i.e. it shouldn't return > > > upon the first detected error. > > > > > > > Of course we could document that streaming off always counts as succeeded > > > > (e.g. decreasing device's runtime PM usage_count) while it could return an > > > > informational error code. But I wonder if anyone would ever benefit from > > > > that somehow. :-) > > > > > > I think it could be useful to propagate errors up to inform the user > > > that something wrong happened. That would involve fixing lots of drivers > > > along the call chain though, so there's no urgency for the ov5645 to do > > > so, but isn't it better to propagate the error code instead of hiding > > > the issue ? > > > > I also don't think hiding the issue would be the best thing to do, but that > > wouldn't likely be a big problem either. > > > > How about printing a warning in the wrapper while returning zero to the > > original caller? This would keep the API intact while still leaving a trace > > on something failing. Of course the driver is also free to print whatever > > messages it likes. > > While I think error propagation could be more useful in the long run, > printing a message in the wrapper is a good idea. I like centralized > error handling, it has a tendency to go wrong when left to individual > drivers. I can send a patch... -- Sakari Ailus